Bone/Joint development Flashcards
What is the name of the process that precedes bone development
Mesenchymal consendation
What is mesenchymal condensation
When previously dispersed mesenchymal cells gather together to differentiate into a single tissue type
In the case of bone, they differentiate into chondroblasts/osteoblasts
What initiates the formation of a joint
Appearance of the interzone & tri-laminar structure
What is the interzone
An intermediate layer of flattened mesenchymal cells
Separates the 2 cartilaginous templates previously formed via mesenchymal condensation
What protein do the interzone cells express
Collagen type I
What is the theory via which joint cavitation occurs
Small tears form in the structurally weak interzone
These are propagated via movement of the joint in utero
What joint factors does mechanical loading in utero affect?
Shape of joint
Cavitation
What is not affected by mechanical loading in utero?
Interzone formation
What 2 types of ossification occur during the development of bone?
Intramembranous ossification
Endochondral ossification
How does the MoA of intramembranous & endochondral ossification differ
Intramembranous: direct differentiation of MSCs into osteoblasts
Endochondral: mineralisation of pre-formed cartilage template
Outline the process of intramembranous ossification
MSCs aggregate and differentiate into osteoblasts
Osteoblasts secrete osteoid matrix which is subsequently calcified
What are the 2 types of intramembranous ossification
Dermal
Perichondral
What type of bones are produced in dermal intramembranous ossification (3)
Skull
Mandible (& most facial bones)
Clavicle
What type of bones are produced in perichondral intramembranous ossification
Periosteal bone collar of long limbs (CORTICAL BONE)
This aids endochondral ossification
Outline the process of endochondral ossification
- Chondrocytes in the centre of the diaphysis become hypertrophied forming 1ry ossification centre
- They release a collagenous matrix which is mineralised
- The calcification causes chondrocytes to die via apoptosis creating a cavity
- Vessels penetrate bringing osteoblasts and osteoclasts to the site
- Osteoblasts produce and mineralise osteoid, osteoclasts remodel to form the medullary cavity
- Chondrocytes at the epiphyses become hypertrophied, forming 2ry ossification centre
- Vessels penetrate the cavity left by dead chondrocytes bringing osteoblasts leading to ossification of the epiphyses
What type of bones are produced in endochondral ossification
Appendicular bones (limbs) Axial bones (those not produced by IO)
Do vertebral bodies contain growth plates
No
How do the VERTEBRAE develop
After endochondral ossification, they are left with cartilaginous plates on their inferior and superior surfaces
Once they are fully grown they reduce the cartilaginous plates to thin layers
Which spinal curvatures are primary and which are secondary
Primary: Thoracic and Sacral (concave/kyphotic)
Secondary: Cervical and Lumbar (convex/lordotic)
When does the cervical and lumbar curves appear
Cervical: When babies begin sitting
Lumbar: When babies begin standing
What type of collagen is produced in intramembranous ossification
Type 1 collagen produced by osteoblasts
What type of collagen is produced in endochondral ossification
Type X collagen matrix produced by the hypertrophic chondrocytes
What is an osteogenic bone graft
A bone graft that contains all the cellular components, growth factors and scaffold necessary to FORM new bone
What is an autogeneous osteogenic bone graft
Bone sample from an individual (usually from iliac crest)
What is an osteoconductive bone graft
This is an acellular graft that serves as a scaffold that can host/support the cells necessary for bone formation
Pathophysiology of Achondroplasia
- Mutation in FGFR-3 gene
* Chondrocytes undergo premature hypertrophy and they fuse before growth can occur
Pathophysiology of Rickets
- Results from a lack of Vitamin D
- Leads to insufficient/delayed mineralisation of growth plates
- Results in reduced compressive strength
- With weightbearing, this results in the distinctive bowing of bones
Pathophysiology of Arthrogryposis
Multiple stiff joints
There is fibrosis of the muscles resulting in restricted movement in utero
Pathophysiology of Developmental Dysplasia of the Hip
Femoral head is not located in acetabular space
More commonly affects left hip
Risk factors of DDH
Family history
Female sex
Mechanical risk factors for DDH (4): All lead to reduced in utero movement
Ligament laxity
Breech presentation
Lack of in utero fluid
Larger baby
